Dry eye syndrome which usually results from inadequate production of the aqueous layer of tears can often be palliated by obstructing the punctum that drain tears into the nose. This is done by means of minuscule punctal spiles or plugs. Each plug features a distal glanduliform or barbed head. The head acts as an anchor and is backed by a short median shank of a cross-diameter substantially smaller than the largest portion of the head, and a broad circular proximal cap which remains outside the punctum and can be seized with tweezers or pincers to extract the plug. The largest cross-diameter of the head must be slightly larger than the cross-diameter of the canaliculus and its opening punctum in order to maintain the plug in its optimal position.
The prior art offers an ophthalmic punctal opening dilatation and plug insertion tool available under the name Ready-Set Punctum Plug from FCI Opthalmics of Marshfield Hills, Massachusettes which consists of a pencil dimensioned member having at one end a dilating reamer and at the opposite end a thin shaft through which runs a small axially translatable rod. The distal extremity of the rod protrudes slightly from the end of the shaft and is sized to penetrate a small axial bore in the proximal face of the proximal cap and thus hold the plug during its insertion into the punctal opening of a canaliculus or other type of meatus. A bi-directional squeeze mechanism in the median portion of the tool withdraws the rod and releases the plug once it has reached the desired position.
The prior art tool suffers from several critical drawbacks.
First, the dilating reamer is constituted by circular shaft of a substantial cross-diameter terminated by an elongated conical spike. The degree of penetration of the spike into a meatus determines the amount of obtained dilation. Although such a dilator has the flexibility of providing an adjustable amount of dilatation, the physician can only estimate how far to push the dilator into the punctal opening. If the dilatation is not sufficient, the insertion of the plug may be painfully difficult or impossible. If the dilatation exceeds the diameter of the proximal cap, the plug may be inadvertently pushed too far into the canaliculus. If the dilatation even exceeds the largest diameter of the anchoring head, the plug may be too loose and soon exit the meatus.
Second, because of the relatively large forces typically required to insert the typically tight-fitting plug, it can be difficult for the physician to judge whether the force is the correct amount needed to seat the plug at the proper optimum depth with respect to the punctum. In other cases the force required to push the plug into the punctum carries the plug too deeply into the canaliculus. Plugs which have been inserted too deeply can be difficult to remove, leading to tissue damage, infections, tearing or other complications. Potentially exacerbating the problem is that the plugs are often made from a soft, flexible material such as silicone often having a durometer of 60 A which will tend to distort under the insertion forces, making it difficult to place the plug properly. The soft cap of the plug cannot prevent the plug from being placed too deeply through the punctum and into the canaliculus. Physicians are taught and follow the practice of pushing with the minimum force possible. However, as noted above, this force can be impossible to accurately judge given the variability inherent in the procedure. In many situations the force required to push the head through the punctal opening causes the entire plug to go too deep.
Third, the prior art bi-directional squeeze mechanism for retracting the rod is located on a part of the tool that the physician will typically need to grasp during insertion. Therefore, when the physician grasps this portion and applies force to the tool to insert the plug through the punctum, it is possible for the physician to inadvertently actuate the squeeze mechanism and prematurely release, or partially dislodge the plug from the tool. Further, because the squeeze mechanism typically requires that the physician's thumb and index finger be located on opposite sides of the mechanism in order to actuate withdrawal of the rod, control of the tool, especially under force is made difficult.
Fourth, in order to keep manufacturing costs low, the disposable body of the tool is often made of injection molded plastic to relatively low dimensional tolerances. During insertion, forces on the rod can cause the soft plug to move in an off-axis manner and buckle within its loose-fitting channel, potentially leading to inadvertent retraction and unintentional premature dislodgement of the plug from the tool.
In addition, the precarious holding of the plug by the small amount of the rod that penetrates the plug may not allow the physician much freedom of action during the insertion process, and often results in the inadvertent, premature separation of the sterile plug from the tool. The plug may be dropped before insertion or left only partially inserted. In the latter instance, another tool must be used to extract the partially inserted plug and re-attach it to the insertion tip in order to attempt a repeat of the insertion procedure. Such procedures can be difficult and time-consuming.
Many surgeons prefer to maximize visualization of the plug during insertion to the extent possible. Devices which seek to stabilize the plug while it is attached to the inserter can tend to obscure the view of the plug. This can lead to an undesirable tradeoff between stability and visibility.
Presently, many prior punctal plug insertion tools use a retractable rod. However, the surfaces guiding the rod allow the rod to bend or buckle as force is applied to the insertion tool during placement of the punctal plug into the punctum. This will then alter the distance between the body of the insertion tool and the plug, resulting in imprecise control over the plug.
Therefore, there is a need for a punctal plug insertion device and method which addresses one or more of the above problems.